The present invention relates to an improved process for the preparation of stannane (SnH4) and deuterostannane (SnD4) from stannic halide and a reducing agent such as lithium aluminum hydride and lithium aluminum deuteride respectively.
Stannane and deuterostannane have been conventionally prepared by reacting stannic halide in the gas phase, neat liquid phase or dispersed in a solvent with a reducing agent, lithium aluminum hydride (LiAlH4) or lithium aluminum deuteride (LiAlD4), respectively in solid form or dispersed in a solvent. Reactions between stannic chloride and these reducing agents are exothermic and the products of the reactions, stannane and deuterostannane, are pyrophoric and the reaction mixtures can deflagrate explosively. These procedures can result in low yields and/or the generation of impurities and the need for purification steps.
A. D. Norman, et al., Inorganic Syntheses Vol. 11, 1968, p. 170, prepared SnH4 and SnD4 by controlled addition of an etherate slurry of stannic chloride to a slurry of LiAlH4 or LiAlD4 in the same solvent at −70° C. The reaction mixture is maintained at −60 to −70° C. This process produced a yield of stannane of about 30% and about 25% for deuterostannane. Extra purification steps are required to remove the stannane and deuterostannane from the ether solvent.
A. E. Finholt, et al., J. Chem. Soc., 1947, 69, 2692, prepared SnH4 by distilling stannic chloride in vacuo into a reaction vessel attached to the vacuum system, and was solidified in a liquid nitrogen bath. After admitting gaseous nitrogen to the apparatus, a solution of LiAlH4 in diethyl ether was added. The mixture was allowed to warm without stirring. At about −30° C. the reaction proceeded vigorously. Volatile material was removed from the reaction zone at ten-minute intervals. The mixture thus removed was immediately condensed and solidified in a liquid nitrogen bath. The volatile materials were fractionated several times. The yield of SnH4 was 20.4%.
H. J. Emeleus and S. F. A. Kettle, J. Chem. Soc. 1958, 2444-2448, prepared SnH4 via a modification of the method described by Finholt, et al. An ether slurry of the stannic chloride-diethyl ether adduct was transferred into the reaction vessel and frozen in liquid nitrogen. An ether solution of LiAlH4 was subsequently added and frozen. A stream of nitrogen containing 0.1% oxygen to inhibit the decomposition of stannane was passed and the reaction vessel was warmed to −78° C. until the ether was liquid and then warmed to −63.5° C. until the solution was brown. The temperature was allowed to increase gradually (1 hr.) to −20° C., and evolution of stannane was then complete. The authors claim that in a typical run they recovered 6.7 grams of stannane from 22.3 grams of ether adduct with stannic chloride and 10 grams of LiAlH4, which we calculate to be about a 78% yield. Further purification of the stannane from diethyl ether is required.
G. W. Schaeffer, et al., J. Am. Chem. Soc. (1954), 76(4), 1203, prepared stannane with yields as high as 84% via sodium borohydride reduction of tin(II) chloride in 0.6 N hydrochloric acid solution. This is an efficient stannane synthesis having a yield as high as 84%. However, the yield drops off sharply as the concentration of tin increases above 1 mg of tin per ml of solution making large batches not practical. At 3 mg of tin per mL of solution the yield of stannane is 37% and at 4 mg per mL of solution the yield is 25%. In addition, it is believed that a small amount of boron hydride impurities may be present in the stannane making it undesirable as a material to be used in microelectronic materials. The crude product was purified by fractionation through a trap maintained at −112° C.
Reifenberg, et al., U.S. Pat. No. 3,867,463; U.S. Pat. No. 3,708,549 and (3) U.S. Pat. No. 3,654,367 describe the preparation of stannane by reacting tin tetrachloride, tin tetrabromide or tin tetraiodide in the presence of a nitrogen atmosphere containing about 0.1% oxygen with LiAlH4. The tin halide is reacted with LiAlH4 and may be carried out with or without an inert diluent solvent. The initial temperature is preferably near −200° C. and is slowly elevated to −70° C. Suitable solvents or diluents may include aliphatic hydrocarbons, aromatic hydrocarbons and ethers. The forgoing may contain carboxylic esters, carboxylic amides and nitrile groups as substituents. Suitable solvents are diethyl ether and tetrahydrofuran. The stannic halide is cryogenically combined with LiAlH4 and slowly warmed to produce stannane. Each patent cites the same example for stannane preparation. Example 1 of these patents describes a reduction of tin tetrachloride with LiAlH4, without solvent and reports a yield of about 87%.
Our laboratory experience in reproducing these methods has resulted in low yields and has periodically resulted in runaway, uncontrolled reactions, which have resulted in deflagration of the reagents and, in some cases, detonations.